Experimentation with nuclear fusion reactions has created a need for handling the deuterium tritium fuel employed. The starting material employed is a mixture of hydrogen isotopes, consisting nominally of equimolar quantities of deuterium and tritium with low levels of hydrogen. In the present invention four product streams are provided. These are (1) an essentially tritium free stream of H.sub.2 and HD wastes for disposal to the atmosphere, (2) a high purity stream of D.sub.2, a stream needed in fusion research for refueling and plasma heating by injection, (3) a stream of basically pure DT for refueling fusion reactors, and (4) a high purity stream of T.sub.2 for refueling and for studies on properties of tritium and effects of tritium on materials. All of the above separations must be performed continuously and reliably over long periods of time.
Cryogenic fractional distillation was selected as the best process for making the required separations due to relatively large separation factors, low power consumption, high throughputs, relatively short start-up times, and flexibility of design.
A system of four distillation columns is required to produce four products of specified purity from a multicomponent mixture. In addition, comparison of the feed stream with the four desired product streams indicates that one component, HT, is in the feed stream and is not desired in any product stream. It is desired, therefore, to discard the H, tritium-free, to the atmosphere and retain the T in the system. Thus, HT molecules must be split, which cannot be done by distillation alone. Destruction of HT molecules is accomplished by two catalytic room temperature equilibrators, which destroy HT in the presence of large quantities of D.sub.2 by promoting the reversible reactions: HT+D.sub.2 .revreaction.HD+DT. Thus the total separation scheme consists of six elements, four cryogenic distillation columns plus two equilibrators.
An important factor involved in the present invention are the characteristics of tritium. Tritium is radioactive, 9270 Ci/g, has a resultant radioactive rate of decay of 0.324 W/g, and is extremely expensive, presently costing approximately $3,000 per gram. As a result of these characteristics, it is highly desirable that the amount of tritium in the system be kept to a minimum.
Two additional important design parameters are the relative volatilities for D.sub.2 /DT/T.sub.2 and the separating efficiency of commercial distillation column packings.